It is well established that exposure to virtual motion environments
(VME) can elicit postural instability (PI) in addition to motion
sickness (MS). While research has found sex differences in
motion sickness, the results of experimental studies are equivocal
regarding these differences, and previous studies utilizing VME
have failed to address the factor of sex differences in terms of
hormonal fluctuations, which may also be instrumental in
behavioral responses to VME, such as PI. The intent of this
investigation was to determine whether exposure to VME, during
various phases of the menstrual cycle (premenstrual,
permenstrual, ovulation) would reveal sex differences in MS and
PI during some phases, but not others. The first experiment
involved men and women completing Daily Living Logs for a
period of 40 days to provide a baseline for any sex differences
(and for women, menstrual phase differences) in motion related
activity and symptomatology. The second experiment involved 24
participants (6 men) viewing a rotating Archimede’s spiral for a
period of twenty minutes. Exposures were timed to place each
woman in three phases of her menstrual cycle; men were exposed
by yoking their exposure time to a female counterpart. Multiple
measures of PI and MS were recorded before, after and during
exposure. Results of the first experiment found no significant
effects of sex or phase upon symptomatology, revealing no
support for the theory of a reporting bias as influencing sex
differences in MS or PI elicited in the laboratory. The second
experiment found no significant effect of sex of phase upon any of
the PI measures, but found significant interaction effects of
sequence and phase, as well as sequence and sex, upon reported
magnitude ratings of illusory self-motion perception. There were
also significant effects of sex found upon measures of MS, with
women reporting more discomfort to exposure to motion
stimulation, as compared to men. There were no significant
effects of phase upon any of the MS measures. While these
findings show no support for a reporting bias influencing the sex
differences found experimentally induced MS, it yields no
evidence to support a hormonal influence on these differences.

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